1. Field of the Invention
This application pertains to liquid chemical transport and dispensing systems. In particular, this invention pertains to apparatus for transporting a substantial quantity of liquid chemical and delivering the chemical at high potential flow rates.
2. Description of the Prior Art
Chemical spraying apparatus in factories finds many applications. Where large quantities of a liquid chemical are to be used at a high rate, transportation of the chemical and subsequent manipulation for use present substantial problems. This situation is apparent in integrated circuit photofabrication. Glass plates having a photographic emulsion are developed to provide master negatives for contact printing on a board having a silicon substrate. The microscopic nature of the circuit image on the glass plate requires exceptional care in handling. Therefore, the plates are processed manually by spraying with suitable photographic development and reversal process chemicals. The susceptibility of the plates to scratches and contamination by dust is such that a single master is only used for about a dozen contact printings. Thus a large number of master plates must be manufactured to meet the demands of the integrated circuit industry, which produces the circuits in extremely high volumes.
In one processing arrangement commonly in use, a 60 gallon drum feeds about 10 hose-coupled nozzles which workers use to spray the plates. The 60 gallon (235 litre) drums commonly used are typically 6 feet (2 meters) high and 3 feet (1 meter) in diameter. The quantity of liquid chemical used is often 15-17 quarts per minute and the dispensing apparatus from the drum must be sufficient to provide this rate of flow.
Although a drum with suitable fittings provides the high flow rate desired in photofabrication, the drum has a number of undesirable aspects. The drums must frequently be changed when usage rates are high, such as 15 quarts of liquid chemical per minute. The drums must be moved from a point of filling to a point of use and the large size causes difficulty in maneuvering. Generally there is an opening at the top of the drum in which a hose may be inserted to add liquid chemical. Drum height makes refilling cumbersome. The bulkiness of the drums invites accidents and injuries to workers.
An extremely tall tank of large volume for providing a high pressure source located adjacent the point of use at a photo-fabrication plant would not be a suitable expedient. Photographic and other chemicals are often unstable or at least subject to change with age or exposure conditions. Large quantities of chemicals are likely to deteriorate or change their properties over the time during which the liquid chemicals in such a tank would be consumed.
Smaller tanks are not suitable for providing a chemical flow with photofabrication since the tanks hold an insufficient quantity of fluid. In the unrelated field of beverage dispensing small tanks have been serially coupled together to increase effective tank storage capacity. However, serial connection limits the potentially available liquid flow rate.
Thus, a convenient chemical dispensing unit which would provide an adequate liquid chemical flow, has a sufficient storage capacity, is easily filled and which would promote worker and factory safety is clearly desirable.